Thirty-one patients with systemic lupus erythematosus had membranous lupus nephropathy (MLN). They were divided into two groups. Group I consisted of 13 patients who had pure MLN but the patients in Group 2 had segmental proliferation in up to 35 per cent of their glomeruli. The rest of the glomeruli had purely membranous change. The patients of Group 2 were no different from the other MLN patients in terms of age, sex and race. The extrarenal disease in both groups was extensive and severe. The renal disease was usually associated with the nephrotic syndrome or oedema but was asymptomatic throughout in one patient. Both renal and extrarenal features responded to treatment initially but relapses were frequent and often severe. Relapses often occurred as treatment was discontinued or medication reduced. Survival at six years in Group I was 62 per cent and in Group 2 was 50 per cent. Only one patient died with renal failure although five patients had impaired renal function at death. The chief causes of death were disease of the central nervous system and infection.